The use of removable seats in an increasing number of motor vehicles is known. This is especially true for vehicles which are known as vans or sports utility vehicles (SUVs) or off-road vehicles. Data relating to airbag diagnostics, airbag ignition, child seat detection and passenger classification is currently transmitted between the chassis and the respective removable seat over flexible cables and plug connectors. The alternative use of inductive transformers, thereby avoiding the disadvantages of plugs, is also known. In this case, the primary side of the transformer is connected to the chassis and the secondary side to the seat. The transformer is designed so that, when installed, it allows for maximum magnetic flux.
The data bus for constraint means according to the present invention has the advantage over the related art that it uses only one data bus to interconnect, for data transfer purposes, the constraint means in the different removable seats or in moving parts. This reduces the number of lines and allows for greater flexibility in responding to changes in the number of, or modifications to, constraint means. Because inductive transmission is used, it is particularly advantageous to use digital transmission with FSK (frequency shift keying) signals, which are easily transmittable via an inductive transformer in the form of AC voltage signals.
It is especially advantageous for the data to be transmitted in a format in which a start bit string is first transmitted, followed by a bus station identifier, and finally the information field for evaluating the bus station identified by the bus station identifier. The start bit string advantageously identifies the beginning of the data message. Via the bus station identifier, any bus station can passively determine whether or not the data message is destined for this bus station, using a simple comparator. The information field can advantageously provide tasks for a particular bus station or contain important information that a further bus station, such as the control unit, needs for further processing.
It is further advantageous, in the event of deployment of the constraint means, for the control unit to signal the deployment to the constraint means over a power supply line. Since the constraint means in this case are connected by transformers, this can be accomplished by a frequency pulse that is sent over the power supply line.
Finally, it is also advantageous for the bus stations connected to the data bus to include means for sending and receiving frequency shift keying signals, using, in particular, phase-locking loops, with these bus stations also using comparators to evaluate the bus station identifiers in the data messages.